As long as the casing sidewall angle, shoulder angle, and distance from case head to shoulder are the same so that the die itself will properly size those areas of the case, then yes it will work. You can go down a couple calibers with the bushings. You may have to back the bushing off a bit because the necks will extend further up into the die body when dropping a caliber or two.
I use a Redding 338 RUM neck sizing style bushing die to resize necks on my 25 RUM. I've dropped about 3 calibers and I do have to back the bushings away from the step in the die or my 257 caliber bushings will crush into the shoulder of the 25 RUM brass. This isn't an S-style Redding die. One of their neck sizing only bushing style dies. But it works fine. I could use it for 300 RUM and 7mm RUM also with the proper bushings.
Like I said, as long as your die, without any bushings installed, will properly resize all the other portions of the wildcat casing then you can use the die with a smaller bushing to resize the necks - ONCE THE NECKS HAVE BEEN SIZED DOWN. The first time you size the necks down you may or may not have a problem. You're not dropping down very much in caliber - so you may get away with sizing the necks down with the smaller bushings. In my case - I use a standard 25 RUM full length sizing die to initially reduce 7mm RUM brass necks down to .257 neck size. After the first sizing and case firing, I use the 338 RUM neck sizer bushing die with bushings for the 25 RUM necks.
I've never tried to cone out a neck bushing and I wouldn't try it if I were you. Those bushings are hardened. No need to do bother with that anyway.
Don't know if you're following this or not. Ask if you have questions.
